Toner containers used in electrophotographic image forming apparatuses are typically made of resin and manufactured through injection molding or blow molding. In blow molding, a hollow parison made of resin is softened by heating and set inside a mold. The inside of the parison is blown with air to draw the parison and make the resin tightly contact an inner face of the mold, thereby shaping the resin into a predetermined shape. For example, Patent Documents 1 to 3 disclose such processes.